This invention relates to an image processing apparatus and method as well as a recording medium, and more particularly to an image processing apparatus and method as well as a recording medium suitable for use with an apparatus which has functions for convergence correction, correction of video distortion and correction of non-uniform brightness or chromaticity of a video.
In recent years, a cathode ray tube display apparatus of the raster scanning system has been popularized as a display apparatus for displaying an image. The cathode ray tube display apparatus corrects images of three colors of, for example, red, green and blue against displacement in superposition to display an image. In the following description, such correction against displacement is referred to as xe2x80x9cconvergence correctionxe2x80x9d.
In such a cathode ray tube display apparatus as described above, convergence correction is performed with a high degree of accuracy popularly using a method wherein convergence correction current is supplied to a convergence correction coil. FIG. 1 shows an example of configuration of a convergence correction apparatus that effects such convergence correction. Referring to FIG. 1, the convergence correction apparatus 1 shown includes an adjustment apparatus 2, a storage apparatus 3, a control apparatus 4, a corrected waveform outputting apparatus 5, an output amplifier 6 and a correction coil 7.
In the convergence correction apparatus 1 shown in FIG. 1, convergence adjustment data are produced by the adjustment apparatus 2 in advance and stored into the storage apparatus 3. The stored convergence adjustment data are read out by the control apparatus 4 and outputted to the corrected waveform outputting apparatus 5 together with synchronization frequency information, raster scan position information and other necessary information determined by the control apparatus 4. The convergence adjustment data inputted to the corrected waveform outputting apparatus 5 are worked based on the synchronization frequency information, raster scan position information and other information so as to allow optimum convergence correction, and then are converted into a convergence correction waveform and outputted to the output amplifier 6. The convergence correction waveform inputted to the output amplifier 6 is amplified in voltage and amplitude and supplied to the correction coil 7 attached to the cathode ray tube so that convergence correction is performed.
Conventionally, roughly two correction waveform generation methods are available including a function generation method and a memory mapping method. The function generation method approximates a convergence correction waveform to a finite function based on information such as convergence correction data at a convergence adjustment point and a synchronization frequency to generate a convergence correction waveform in synchronism with raster scanning of the cathode ray tube. According to the function generation method, the memory capacity for storing adjustment data may be smaller than that of the memory mapping method. Therefore, the function generation method is advantageous in that it can be produced at a comparatively low cost, but is disadvantageous in that it is low in degree of freedom in correction.
Meanwhile, according to the correction waveform generation method of the memory mapping method, a display screen is divided into gratings, and regarding each grating point as an adjustment point, a convergence correction amount necessary for the adjustment point is stored into a memory in advance. Then, at each grating point, the corresponding adjustment data stored in the memory is read out, but at any other point, correction data is obtained by interpolation processing using a straight line or a quadratic curve based on the correction data at the grating points, and is used to generate a convergence correction waveform. The memory mapping method exhibits a higher degree of freedom in correction and allows correction of convergence with a higher degree of accuracy than the function generation method. Therefore, particularly a display unit for which a high display quality is required such as, for example, a display unit for a computer frequently uses the memory mapping method.
It is popularly known that a position error of a video displayed on a cathode ray tube can be corrected by adjusting the output timing of video signal data. FIGS. 2A and 2B illustrate horizontal linearity correction by adjustment of the output timing of video data in a horizontal period. Particularly, FIG. 2A illustrates a displayed video when a position error is not corrected, and FIG. 2A illustrates a displayed video when the output timing of video signal data is adjusted to perform horizontal linear correction. Where the horizontal deflecting current is distorted, when no correction is performed, the horizontal linearity is distorted as seen in FIG. 2A, but when the video signal is adjusted in a direction of the time base so as to correct the distortion of the horizontal deflecting current, the horizontal linearity can be corrected as seen in FIG. 2B.
In the example illustrated in FIGS. 2A and 2B, the output timing of video signal data is adjusted in a horizontal period. However, if the output timing is adjusted in a vertical period, then correction of image distortion in a vertical period can be performed in a similar manner.
FIG. 3 shows an example of a display apparatus which performs such deflection correction as described above with reference to FIGS. 2A and 2B. Referring to FIG. 3, the display apparatus 10 shown includes a memory 11, a digital/analog (D/A) conversion circuit 12, a correction circuit 13, a clock (CLK) generation circuit 14 for generating an adjustment clock signal, a video circuit 15, a deflection circuit 16, a horizontal deflecting coil 17, a measuring resistor 18 for detecting horizontal deflecting current, a vertical deflecting coil 19, and a cathode ray tube 20.
An input video signal is written into the memory 11 at a timing of a first clock signal clk1. Then, the image data written in the memory 11 are read out at another timing of a second clock signal clk2 and converted into an analog video signal by the D/A conversion circuit 12, whereafter they are inputted to the video circuit 15. The image signal inputted to the video circuit 15 is amplified by the video circuit 15 and applied to the cathode of the cathode ray tube 20.
On the other hand, the correction circuit 13 produces a reference signal for horizontal deflecting current in synchronism with a synchronizing signal. The reference signal produced is written into the memory 11 at a timing of the first clock signal clk1 similarly to the video signal, and is then read out from the memory 11 at another timing of the second clock signal clk2, converted into an analog video signal by the D/A conversion circuit 12 and inputted to the clock generation circuit 14.
Meanwhile, the synchronizing signal inputted to the deflection circuit 16 to drive the horizontal deflecting coil 17 and the vertical deflecting coil 19 to form a raster on the cathode ray tube 20. The measuring resistor 18 is a detecting resistor for measuring the horizontal deflecting current, and a voltage which increases in proportion to the horizontal deflecting current is inputted from the measuring resistor 18 to the clock generation circuit 14. The clock generation circuit 14 compares the detection voltage of the horizontal defection current inputted thereto from the measuring resistor 18 with the reference waveform of the adjusted horizontal deflecting current inputted thereto from the D/A conversion circuit 12 through the memory 11 and supplies an amplified waveform of a difference between the two input waveforms to a voltage-controlled oscillator (VCO). The VCO generates a second clock signal clk2 adjusted in accordance with the difference between the two input waveforms and supplies the second clock signal clk2 to the memory 11 and the D/A conversion circuit 12.
Through the series of operations described above, the second clock signal clk2 is adjusted so that the difference between the reference waveform of the horizontal deflecting current and the waveform of the actual deflecting current may be minimized. Consequently, the video signal inputted to the cathode of the cathode ray tube 20 is adjusted in the direction of the time base so as to correct the distortion of the horizontal deflecting current thereby to correct the position error of the video.
In the system described above, a reference waveform of horizontal deflecting current and the waveform of actual horizontal deflecting current are compared with each other, and the difference between the waveforms is fed back to adjust the clock signal so that the difference may be eliminated. As a result, also the output timing of video signal data is adjusted to correct the position error of the video.
In the convergence correction described above, the output amplifier 6 is used to supply correction current to the convergence correction coil 7 with reference to a convergence correction waveform produced by the function generation method or the memory mapping method to correct the convergence. However, in order to perform such convergence correction, high current must be supplied to the correction coil 7 for convergence correction. Therefore, it is difficult to miniaturize the correction coil 7, the output amplifier 6 for driving the correction coil 7 and pertaining elements, and there is a subject to be solved in that miniaturization of the convergence correction apparatus 1 itself is difficult.
Also it is a subject that the power loss of the output amplifier 6 is great. Further, in order to correct the convergence with a high degree of accuracy, a system is required which has an increased number of adjustment points like the memory map method and has a high degree of freedom in correction. Actually, however, phase delay of convergence correction, interference between adjustment points and so forth are caused by a limitation to the slew rate characteristic of the output amplifier, eddy current loss in the inside of the cathode ray tube and other parameters. Thus, there is a subject to be solved in that further augmentation of the accuracy in correction of the convergence is difficult.
On the other hand, where such a method of correcting the position error of a video on the display of the cathode ray tube by adjusting the output timing of video signal data as described above is used to perform correction of distortion of an image, a raster which is not uniform in density appears as seen in FIG. 4 and makes the brightness non-uniform. Further, since the position error is detected from the waveform of horizontal deflecting current, although correction of distortion of an image can be performed, the position errors of the three colors of red, green and blue cannot be detected, and there is a subject to be solved in that the convergence cannot be corrected.
It is an object of the present invention to provide an image processing apparatus and method by which miniaturization and reduction in power consumption of a convergence correction circuit and a deflection circuit can be achieved.
It is another object of the present invention to provide an image processing apparatus and method by which correction of convergence and video distortion and correction of non-uniformity of the brightness and the chromaticity can be performed with a high degree of accuracy.
In order to attain the objects described above, according to the present invention, the output timings of video signals of red, green and blue are adjusted independently of one another to correct the position errors of the three videos individually.
According to an aspect of the present invention, there is provided an image processing apparatus, comprising inputting means for inputting a plurality of video signals corresponding to different colors therethrough, storage means for storing the video signals inputted through the inputting means, production means for producing correction data to be used for correction of convergence, generation means for generating a clock signal for each of the video signals corresponding to the different colors based on the correction data produced by the production means, and readout means for reading out the video signals stored in the storage means in response to the clock signals generated by the generation means.
The video signals inputted through the inputting means may correspond at least two of a video signal of red, another video signal of green and a further video signal of blue.
The video signals inputted through the inputting means may be digital video signals which are digital video signals obtained by conversion of analog video signals, digital video signals transmitted and decoded by transition minimized differential signaling (TMDS), digital video signals transmitted and decoded by low voltage differential signaling (LVDS) or digital video signals transmitted and decoded by giga-bit video interface (GVIF).
The image processing apparatus may further comprise arithmetic operation means for arithmetically operating a correction parameter to be used for correction of image distortion from data which include at least one of synchronizing signal data, video size data and video phase data, the generation means generating the clock signals further based on the correction parameter.
In this instance, the image processing apparatus may further comprise conversion means for converting the video signals inputted through the inputting means into video signals whose non-uniformity in brightness and chromaticity are corrected based on the correction parameter arithmetically operated by the arithmetic operation means.
According to another aspect of the present invention, there is provided an image processing method, comprising a storage control step of controlling storage of a plurality of video signals corresponding to different colors, a production step of producing correction data to be used for correction of convergence, a generation step of generating a clock signal for each of the video signals corresponding to the different colors based on the correction data produced by the processing in the production step, and a readout control step of controlling reading out of the video signals, whose storage has been controlled by the processing in the storage control step, in response to the clock signals generated by the processing in the generation step.
According to a further aspect of the present invention, there is provided a recording medium on which a computer-readable program is recorded, the program comprising a storage control step of controlling storage of a plurality of video signals corresponding to different colors, a production step of producing correction data to be used for correction of convergence, a generation step of generating a clock signal for each of the video signals corresponding to the different colors based on the correction data produced by the processing in the production step, and a readout control step of controlling reading out of the video signals, whose storage has been controlled by the processing in the storage control step, in response to the clock signals generated by the processing in the generation step.
With the image processing apparatus, the image processing method and the recording medium, a plurality of video signals corresponding to different colors are stored, and correction data to be used for correction of convergence are produced. Then, a clock signal is generated for each of the video signals corresponding to the different colors based on the correction data, and the stored video signals are red out in response to the generated clock signals.
Consequently, miniaturization of a convergence correction circuit and a deflection circuit and reduction of the power consumption can be anticipated, and besides convergence correction can be performed with a high degree of accuracy.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.